boiling water (i gram KOH per litre) until the nitrate no longer becomes
turbid on acidification and finally with boiling water until the alkalinity
is removed. The contents of the filter are washed by means of a fine water
jet into a small porcelain dish, the water being evaporated and the residue
dried at 100° and heated for 10 minntes on a boiling water-bath with 10
c.c. of fuming sulphuric acid (D 1-88). The dish is subsequently left in a
moist place for 12 hours, the contents diluted with 200 c.c. of cold water,
and when cold the anthraquinone filtered, washed as before, placed in a
tared dish, evaporated, dried at 100° and weighed. For greater exactness
the anthraquinone is evaporated and the residual ash determined : anthra-
quinone X 0-8558 = anthracene.
2. Detection of Impurities.—Among the more common impurities
which are harmful in certain applications of crude anthracene, e.g., in the
preparation of alizarin, are methylanthracene, carbazole, paraffin wax
and phenanthrene. These substances are detected as described in the
following paragraphs; for their .quantitative determination, which is
carried out only rarely and for special purposes, special works must be
(a) METHYLANTHRACENE. When anthracene containing methylanthra-
cene is oxidised by chromic acid, as described above, methylanthraquinone
is produced, this forming threads variously twisted rather than needles
like anthraquinone. Methylanthraquinone is distinguished from the latter
also by its great solubility in benzene.
(&) CARBAZOLE. The anthracene is extracted with ethyl acetate, the
solution evaporated, and the residue treated with a few drops of ethyl
acetate to which are added some drops of nitrobenzene and a little phenan-
threnequinone. The presence of carbazole is shown by the formation of
characteristic, lamellar, copper-coloured crystals.
(c) PARAFFIN WAX. 10 grams of anthracene are treated with 100 c.c.
of ether, the ethereal solution separated and evaporated and the residue
treated with 200 grams of fuming sulphuric acid (20% of anhydride) for
three hours at 100°. The whole is poured into 500 c.c. of water and, after
cooling, the paraffin wax separated at the surfa.ce is filtered off, washed
well with water, the filter allowed to dry and then moistened with alcohol,
and the paraffin collected by adding ether. The ethereal solution thus
obtained is evaporated, and the residue, dried at 105°, gives the solid paraffin
in the sample.
(<#) PHENANTHRENE. A certain quantity (i kilo) of the product to be
tested is dissolved in the hot with double its volume of toluene. After
cooling, the crystallised anthracene and carbazole are separated and the
mother-liquor distilled, the portion passing over between 300° and 340°—
which contains the greater part of the phenanthrene—'being collected
apart. 20 grams of this fraction are boiled for half an hour in a reflux
apparatus with 30 grams of picric acid and 300 c.c. of xylene and the liquid
allowed to cool for 24 hours ; the phenanthrene picrate which separates
is crystallised from alcohol in reddish-yellow needles melting at 145°.
1 Lunge : Coal-Tar and Ammonia (London, 1916), p. 640. ^